The invention relates to an improved procedure for facilitating the cold-forming of metals, more particularly iron and steel, by phosphatizing and subsequent treatment with an aqueous lubricant having a soap base.
It has been known for many years to use phosphatizing to facilitate the cold-forming, without machining, of metals. The processes by far the most frequently used in all types of cold-forming are zinc-phosphatizing systems, mainly processes accelerated with nitrate, vitrite and chlorate. Manganese-phosphatizing processes have also been used for difficult cold-forming operations. Zinc-calcium processes and alkali-phosphatizing processes are also used occasionally for specific applications.
During cold-forming, phosphate coatings provide a good separating effect between the tool and the surface of the metal, but a decisive factor, in addition to this, is the avantageous effect of the coating upon the lubricants used. Considerable use is made in practice of the lubricants having a soap base in conjunction with phosphate coatings. For example, alkali soaps can partly transform zinc-phosphate coatings on the workpiece in such a manner as to produce a highly effective zinc soap.
The reaction is generally obtained by immersing the phosphatized and rinsed workpieces in an aqueous saponifying bath, at temperatures of between 70.degree. and 80.degree. C. for between 2 and 5 min. A far-reaching reaction, and therefore better conversion, are sought with specially reactive soap lubricants, the immersion baths containing more than 2% thereof and having a pH value of between 8 and 10. It is possible in this way to obtain total soap deposits of up to about 5 g/m.sup.2 which adhere well to the workpiece, with simultaneous conversion to zinc soap which may then constitute up to 50% of the total coating of lubricant. The coating of soap also contains unreacted alkali soap, especially sodium soap, since it is customary to use sodium-soap baths. The concentration of the soap baths is usually between 2 and 5%. The lubricating properties may often be improved by adding to the solutions inorganic pigments, for example graphite, molybdenum disulphide, borax, sodium pyrophosphate, or metal soaps which are difficult to dissolve, such as calcium-, aluminum, or barium-stearate. The use of surfactant substances, e.g. alkoxylated alkyl phenols, has been found to improve the dispersion of pigments having a metal-soap base.
In many cases, however, e.g. for difficult cold-forming operations such as cold-extrusion, total soap deposits of up to 5 g/m.sup.2 are not adequate, since the formed parts exhibit striations. Considerably thicker total-soap deposits are therefore desired. It is known that the amount of soap deposited may be increased by increasing the concentration of the soap bath, raising the pH value thereof, using a soap containing a large proportion of C.sub.18 soaps, or lowering the temperature of the bath until the soap solution is all most solid. However, none of these steps has been found satisfactory in practice since, in spite of the increase in the weight of the soap deposit, it is impossible to achieve uniform coverage, and the layer of soap does not adhere well to the phosphate base. It is then easily stripped during cold-forming. Furthermore it builds up on the presses which therefore become dirty and need frequent cleaning. This is not only costly, but the material wasted by build-up on the presses is an additional loss factor leading to uneconomical results.
It is therefore the purpose of the invention to provide a procedure which leads, in processes of the type described hereinbefore, to increased total-soap deposits with better adhesion and uniformity, and therefore to improved technical effectiveness and increased economy.